Failed Spark Plug causes cylinder damage

[jrsAudiA6]

So, about 2 weeks ago my wife was leaving to run some errands when she called me to let me know there was a problem with her A5SB and a light was on on the instrument cluster. It turns out the car was miss firing on cylinder 3. I found that the spark plug for that cylinder was missing most of its center electrode insulator. Bought a new spark plug the following day and installed it. The engine ran better but was still miss firing at idle. Took it to the dealer to have them bore scope and compression test that cylinder. The tech took 2 pictures showing scoring to the cylinder walls and damage to top edge of the piston. The compression results were 90PSI for cylinder 3 and 175PSI for the other 3 cylinders. This engine has only 22K miles as it was replaced in early January of 2021, another story that was covered in another thread.

Does anyone know if the the block can be re-sleeved?

What other ideas do you have repair this engine?

[Daaavid]

Disclaimer: I do not have the answers to your question, but I am more interested in the spark plug failure to prevent similar pitfalls with my tune experience. I recall your thread regarding the replacement engine(s) with APR's tune.

• What spark plugs were you running that failed?
• How many miles were on those spark plugs before you replaced them?
• What coil packs are you running?
• Were you tuned when this failure occurred?

I am running Unitronic's Stage 1 Plus tune and I am concerned because I've seen some failures from certain "performance-recommended" spark plugs for tuned 2.0T B9s. Supposedly, RS7 spark plugs are the recommendation and there have been reported failures of this plug in the same fashion you describe. FWIW, I am running OEM NGK RS7 spark plugs with OEM RS3 coil packs.

[jrsAudiA6]

Disclaimer: I do not have the answers to your question, but I am more interested in the spark plug failure to prevent similar pitfalls with my tune experience. I recall your thread regarding the replacement engine(s) with APR's tune.

• What spark plugs were you running that failed?
• How many miles were on those spark plugs before you replaced them?
• What coil packs are you running?
• Were you tuned when this failure occurred?

I am running Unitronic's Stage 1 Plus tune and I am concerned because I've seen some failures from certain "performance-recommended" spark plugs for tuned 2.0T B9s. Supposedly, RS7 spark plugs are the recommendation and there have been reported failures of this plug in the same fashion you describe. FWIW, I am running OEM NGK RS7 spark plugs with OEM RS3 coil packs.

This particular failure occurred with the new engine. So, the spark plugs came with the new engine. They are marked VW AG NGK.
I had not replaced them at the time of failure as the new engine only had ~22K miles.
The coil packs are stock OEM packs.
The new engine was not tuned.
Here are few pics of the failed spark plug.
IMG_0972[1].jpgIMG_0978[1].jpgIMG_0979[1].jpg
As with the previous piston failure, this spark plug failure is probably due to a manufacturing defect in the ceramic/porcelain insulator.
I have not decided on how I am going to fix this issue but I am currently leaning towards purchasing a used A5B9 (engine code CYMC) engine off ebay and either putting that engine in the car or replace the block with the used engine block and putting in new forged pistons. I suppose I may still replace with a new engine. It just sucks that it does not seem possible to repair the damaged cylinder and then replace the damaged piston.

[djkyky]

I had a spark plug failure on my 18 Q7. No tune but this may be an issue with Audi plugs. My car went into limp mode while I was on the Interstate. Not a fun situation. Dealer had my car for two days. It doesn’t appear to have done any damage.

UPDATE:

The engine started misfiring during fast acceleration. Since it was out of warranty with $42k miles I decided to change all the spark plugs. Odd thing was two of the plugs had a sticky oily coating on the threads and the other four plugs had dry threads. No oil above the seal ring or in the plug port of the cylinder head. Plug tips and ground electrodes all looked good. Replacing all the spark plugs fixed the misfire with a noticeable performance improvement.

[jrsAudiA6]

I had a sparkplug failure on my 18 Q7. No tune but this may be an issue with Audi plugs. My car went into limp mode while I was on the Interstate. Not a fun situation. Dealer had my car for two days. It doesn’t appear to have done any damage.

You were very fortunate. Any idea what the failure was with the spark plug?

[djkyky]

They didn’t give details. Just that the plug failed.

[jrsAudiA6]

Update on my wife's A5 damaged cylinder due to broken spark plug:

I was unable to find a bare block for this engine type (cymc). I was able to find a low mileage used cymc engine on ebay that also had the transmission attached. It was located back in Virginia so I was able to have my brother meet with the seller and visually check it out. Based on his assessment he purchased it for me and I am now waiting on it getting shipped to the shop that is going to do the woek. The price for the engine/transmission with 9K miles was only $4500 plus tax and shipping. The seller originally purchased it about 2 years ago with the purpose of putting it into an older model Audi. That did not happen so he sold it.

If this goes as expected I will now have a backup transmission and an engine that perhaps over time I can repair and have as a backup. Wish me luck that this engine is as good as it looks. I know there is always a risk going this route but really did not have much of a choice. Already had to put out 18K to replace the first engine when a piston broke on the original engine and Audi would not cover the cost once they found the engine had a tune.

[Daaavid]

Thanks for the update on this saga.

This was posted on a Facebook group of an OEM NGK RS7 plug that I mentioned last month, albeit this individual's vehicle was tuned. Is this what it looked like when you removed the damaged plug?

[jrsAudiA6]

Thanks for the update on this saga.

This was posted on a Facebook group of an OEM NGK RS7 plug that I mentioned last month, albeit this individual's vehicle was tuned. Is this what it looked like when you removed the damaged plug?

No, there are pictures of my failed spark plug in this thread. The RS7 plug failure has had it's ground electrode burned away, it would appear. This could be an issue with the tune on the RS7. Were as on my failed plug the issue was the center electrode insulator broke in sufficiently small pieces that they fell into the cylinder and damaged the cylinder wall and edge of the piston.

[jrsAudiA6]

Update:

I decided to purchase a "new" used engine (type CYMC) from ebay. I was fortunate enough to come across one that had only 9K miles and it came with a transmission attached along with turbo, alternator and AC compressor, all for $4500. It was located in Virginia which allowed me to have my brother check it out and purchase if he felt was a good deal. The purchase was made and it was shipped to the shop in SoCal. The car is not complete as of this update but the engine has been put in the car and started and allowed to idle up to operating temperature. So far so good, hope to get the car back on Monday as there was other work that was being done. I will be keeping the transmission as it is a low mileage tranny and may come in useful in the future or possibly sell it. The overall cost of all this will be between $10K and $11K. Significantly cheaper than replacing with a new engine.

Edit:

We received the car from the shop Monday morning. I have not driven it yet but my wife tells me it is driving silky smooth. Interesting tidbit the shop told me, they put new plugs in the engine and when removing the old plugs found one was missing. Of course that had them a little worried but went ahead and put in the new ones and fired it up and it ran like a champ. Whew!!!! Saved myself about 6-7 $k going with this used engine vs. a new one. Hopefully no more weird failures that damage the engine internals.